Power amplifiers are among the important components of most communication systems. Wireless communication systems typically employ power amplifiers to compensate for attenuation that occurs during transmission through a propagation medium. One design consideration is that the power amplifier itself may introduce distortion of the transmitted signal as well as lower signal-to-noise ratio levels. Spectral efficiency is also an important consideration in the design of communication systems. Modern second- and third-generation communication systems that have complex digital modulator technologies now demand that linearity also be treated as a critical performance requirement. Thus, both linearity and spectral efficiency are important performance requirements of power amplifiers.
Increasing linearity of a power amplifier is a challenging engineering problem and is usually achieved at the expense of power efficiency. Several techniques have been used to increase the linearity of power amplifiers. One approach, known as digital baseband predistortion, operates based on an adaptation of a function created from the desired modulation level and the power amplifier output.
One popular digital baseband predistortion technique is to use look-up tables to modify amplitude and phase values of the input to a power amplifier. It has been found that the performance of look-up table-based digital baseband predistortion decreases as the operating bandwidth of the power amplifier increases. Consequently, look-up table-based techniques suffer from poor performance in wideband applications.
Given its high computational complexity, digital baseband predistortion using standard polynomial signal processing is also not particularly well-suited to linearizing wideband power amplifiers. One reason for the high computational complexity is the inherent inefficiency of using a sufficiently deep memory and a high-enough polynomial order to span the multi-dimensional signal space needed to mitigate power amplifier-induced nonlinear distortion.